1. Field of the Invention
This invention relates to the preparation of hardenable cross-linked resins. More especially, this invention relates to a hardenable cross-linkable resinous composition consisting essentially of at least one chlorinated or brominated xylyleneglycolbisallylether which has been chlorinated in the nucleus, a maleic acid anhydride and an epoxy compound. This invention is particularly directed to improving the preparation of cross-linked hardenable resins from nucleus chlorinated or brominated xylyleneglycolbisallylethers and maleic acid wherein the resin is modified by the inclusion of an epoxy compound. This invention is particularly directed to formed articles of such a cross-linked polymer having high thermal stability of shape and having excellent flame self-extinguishing properties.
2. DISCUSSION OF THE PRIOR ART
The bisallylethers of xylyleneglycols which have been chlorinated or brominated in the nucleus have been known. These can be prepared, for example, by the procedure described by Stallings et al. (J. Polymer Sci. A-1 (1970), 8, p. 1557). A similar procedure can be used in the preparation of the nonhalogenated bisallylethers.
In the article there is described the reaction of tetrachloro-p-xylyleneglycolbisallylether with maleic acid anhydride employing the composition in a molar ratio of 1:1. The reaction is carried out in the presence of di-tert.-butylperoxide at 95.degree. C and forms a clear, hard copolymer. The copolymer is apparently one in which a sizeable percentage of the maleic acid anhydride is not completely incorporated therein since 40% of the maleic acid anhydride content could be dissolved out of the copolymer by extraction with water.
Recent experiments have revealed that it is difficult to control the cross-linking polymerization of tetrachloroxylenebisallylethers maleic acid anhydride. For instance, when such a resinous composition is subjected to cold hardening no product is formed unless the composition is heated at a temperature up to about 80.degree. C. It is only at this temperature employing equivalent amounts of maleic acid anhydride and bisallylether that a clear melt is formed. This melt solidifies immediately upon cooling to 70.degree. C.
Attempts have been made to form articles by use of a hot setting process by subjecting the composition to temperatures ranging around 80.degree. C in the presence of radical formers. Unfortunately, the cross-linking polymerization is highly exothermic and as a rule is so violent even at the commencement of a reaction that a considerable temperature rise is experienced. The rise in temperature is so great that decomposition of the resin occurs resulting in foaming and great discoloration.
To make useable castings, the uncontrollable setting will have to be controlled either by intense external cooling of the molds or by use of a smaller quantity of initiator, e.g., about 0.01% by weight. Another alternative lies in performing the process without the use of radical formers, but such process requires setting times in excess of 10 hours. None of the foregoing methods are easy to practice on a technical or commercial scale.
The foregoing is unfortunate inasmuch as hardened castings made from tetrachloro-p- or m-xylyleneglycolbisallylethers and maleic acid anhydride (molar ratio 1:2) when shaped and set at a temperature of 80.degree. C and cured at 140.degree. C to have good mechanical characteristics. The Martens thermal stability as measured on a standard specimen is 130.degree.-140.degree. C on the basis of ISO/R 75 A, a thermal stability of shape of 145.degree. to 160.degree. has been found. The bending strength of such a formed article can be 500 to 700 kp/cm.sup.2 and the impact toughness ranges from 5 to 7 cm.kp/cm.sup.2 as measured on the standard specimen. However, it has been found that the resistance of the castings to hydrolysis is quite poor. When the castings are left in water at 100.degree. C cracks form within 48 hours. When a sample is left in a normal aqueous caustic soda solution at 100.degree. C is completely destroyed.
It has therefore become desirable to provide an improved hardened or cast article of a cross-linked resin having components of a tetrachloro-p or m-xylyleneglycolbisallylether and maleic acid anhydride. It has also become desirable to provide an improved process for obtaining such material which obviates the necessity to control the cross-linking polymerization during the setting process. Stated differently, it has become desirable to provide a controlled process for the preparation of cross-linked polymers of such nuclearly halogenated xylyleneglycolbisallylethers or ether containing polymers. More especially, it has become desirable to provide a process for the controlled preparation of such composition which process provides an improved composition-improved in respect of hydrolysis resistance and resistance to aqueous caustic solutions.